The present invention relates to a method and apparatus for determining a particle response characteristic of a device in order to model the degree to which contaminants present within a fluid passing through the device will be delayed or retained within the device. More particularly, the present invention relates to such a method and apparatus in which pulses of particles are introduced into a fluid before the fluid passes into the device to derive statistically repeatable reference and response pulses which form the particle response characteristic of the device.
Ultra-high purity gases pass through much of the equipment, for example, process piping, valves, flow meters, rapid thermal processors and etc. used in the manufacture of semiconductors. Prior to use, the equipment is purged with an ultra-high purity gas to eliminate possible contaminants. For instance, during the loading of wafers into a process chamber of a rapid thermal processor, the process chamber is exposed to ambient air. Air, however, contains moisture which is an undesirable contaminant in the semiconductor manufacturing process. Therefore, the process chamber is purged with an inert stream of gas, generally composed of ultra-high purity nitrogen. In order to insure that the wafers will be processed in a moisture-free environment, the dry down characteristics of the process chamber are measured with a moisture analyzer to determine the length of time required to purge the process chamber so that a sufficiently low level of moisture will exist within the process chamber.
During the purging, the manufacturing process is at a standstill and thus, it is important to minimize the time spent in purging such equipment. As far as is known by the inventor herein, there is no test apparatus or method that can be used to select or design equipment so that the equipment will have the lowest possible retention of contaminants and thus, have the lowest purge time. Another problem relates to the sampling of the purge gas to insure that no contaminants are present in the equipment of interest. For instance, during the determination of the drydown characteristics of a rapid thermal processor many independent observations are made of the moisture content of the purge gas flowing from the process chamber. However, there is no known way to insure that observations are being made that take into account the time resolution capability of the sampling system; in other words, the degree to which piping and equipment used in connection with the sampling system are retaining contaminants such as moisture.
As will be discussed, the present invention provides a method and apparatus for modeling the degree to which a particular device will retain fluid borne contaminants by determining a particle response characteristic of the device.